1. Field of the Invention
The present invention relates to an automatic voltage regulator to automatically keep an output voltage of a generator constant.
2. Description of the Related Art
Conventionally, there exists an automatic voltage regulator to keep an output voltage of a generator to be a set voltage by comparing a detection voltage with the set one of the generator by a comparator and controlling an exciting current of the generator depending on their difference, and another automatic voltage regulator as below is proposed in order to solve a weak point that the output voltage largely overshoots a rated voltage just after a start of the generator.
As shown in FIG. 7, this automatic voltage regulator 80 is equipped with a detection means 83 for detecting that a motor 81 (engine) has been stabilized to a rated speed, a preset circuit 85 for giving a comparator 84 a preset voltage lower than a set voltage based on a detection result of the detection means 83 instead of the set voltage, an exciting current supply means 86 for supplying an exciting current in response to a detection of the detection means 83, a timer 87 for detecting a lapse of constant time after the detection of the detection means 83, and a change means 88 for changing a voltage given to the comparator 84 depending on detection time of the timer 87 from the preset voltage to the set voltage (see columns [0008] to [0010] and FIG. 1 in Japanese Patent Laid-Open Publication No. Hei 5-284799).
However, although the automatic voltage regulator 80 is configured so as to perform a change from a preset voltage to a set one just after a start of the generator 82 depending on the detection time of the timer 87, the regulator 80 has a problem that it cannot surely suppress an overshoot since the preset voltage is not given depending on a detection voltage.
In addition, the regulator 80 has another problem in conditions of a load short circuit and a heavy load application (hereinafter referred to as “the load short-circuit condition and the like”) that it cannot suppress an overshoot due to a release of their causes.